The present invention relates generally to an apparatus and method for the preparation and delivery of gas-enriched fluids to gas-depleted locations, and more particularly, to a system and method for the preparation and delivery of physiologic solutions for treating conditions such as tissue ischemia and post-ischemic tissues, including, inter alia, a catheter for delivering oxygen-enriched blood to specific locations within a patient""s body.
Oxygen is a crucial nutrient for human cells. Cell damage may result from oxygen deprivation for even brief periods of time, which may lead to organ dysfunction or failure. For example, heart attack and stroke victims experience blood flow obstructions or diversions that prevent oxygen from being delivered to the cells of vital tissues. Without oxygen, the heart and brain progressively deteriorate. In severe cases death results from complete organ failure. Less severe cases typically involve costly hospitalization, specialized treatments and lengthy rehabilitation.
Blood oxygen levels may be described in terms of the partial pressure of the oxygen dissolved in the blood (pO2). Typically, for arterial blood, normal blood oxygen levels (i.e., normoxia or normoxemia) range from 90-110 mm Hg. Hypoxemic blood (i.e., hypoxemia) is arterial blood with a pO2 less than 90 mm Hg. Hyperoxic blood (i.e., hyperoxemia or hyperoxia) is arterial blood with a pO2 greater than 400 mm Hg (see Cason et. al (1992), Effects of High Arterial Oxygen Tension on Function, Blood Flow Distribution, and Metabolism in Ischemic Myocardium, Circulation, Vol. 85, No. 2, pp. 828-838), but less than 760 mm Hg (see Shandling et al. (1997), Hyperbaric Oxygen and Thrombolysis in Myocardial Infarction: The xe2x80x9cHOT MIxe2x80x9d Pilot Study, American Heart Journal, Vol. 134, No. 3, pp. 544-550). Hyperbaric blood is arterial blood with a pO2 greater than 760 mm Hg. Venous blood typically has a pO2 level less than 90 mm Hg. In the average adult, for example, normal venous blood oxygen levels range generally from 40 mm Hg to 70 mm Hg.
Blood oxygen levels also might be described in terms of hemoglobin saturation levels. For normal arterial blood, hemoglobin saturation is about 97% and varies only slightly as pO2 levels increase. For normal venous blood, hemoglobin saturation is about 75%.
In patients who suffer from acute myocardial infarction, if the myocardium is deprived of adequate levels of oxygenated blood for a prolonged period of time, irreversible damage to the heart can result. Where the infarction is manifested in a heart attack, the coronary arteries fail to provide adequate blood flow to the heart muscle.
Treatment of acute myocardial infarction or myocardial ischemia often comprises performing angioplasty or stenting of the vessels to compress, ablate or otherwise treat the occlusion(s) within the vessel walls. For example, a successful angioplasty increases the size of the vessel opening to allow increased blood flow.
Even with the successful treatment of occluded vessels, a risk of tissue injury may still exist. During percutaneous transluminal coronary angioplasty (PTCA), the balloon inflation time is limited by the patient""s tolerance to ischemia caused by the temporary blockage of blood flow through a vessel during balloon inflation. Reperfusion injury also may result, for example, due to slow coronary reflow or no reflow following angioplasty.
For some patients angioplasty procedures are not an attractive option for the treatment of vessel blockages. Such patients typically are at increased risk of ischemia for reasons such as, poor left ventricular function, lesion type and location, or the amount of the myocardium at risk. The treatment options for such patients thus include more invasive procedures such as coronary bypass surgery.
To reduce the risk of tissue injury typically associated with treatments of acute myocardial infarction and myocardial ischemia, it is usually desirable to deliver oxygenated blood or oxygen-enriched fluids to at-risk tissues. Tissue injury is minimized or prevented by the diffusion of the dissolved oxygen from the blood or fluids to the tissue and/or blood perfusion that removes metabolites and that provides other chemical nutrients.
In some cases, the desired treatment of acute myocardial infarction and myocardial ischemia includes perfusion of oxygenated blood or oxygen-enriched fluids. During PTCA, for example, tolerated balloon inflation time may be increased by the concurrent introduction of oxygenated blood into the patient""s coronary artery. Increased blood oxygen levels also may cause the normally perfused left ventricular cardiac tissue into hypercontractility to further increase blood flow through the treated coronary vessels.
The infusion of oxygenated blood or oxygen-enriched fluids also may be continued following the completion of PTCA treatment or other procedures (e.g. surgery) wherein cardiac tissue xe2x80x9cstunningxe2x80x9d with associated function compromise has occurred. In some cases continued infusion may accelerate the reversal of ischemia and facilitate recovery of myocardial function.
Conventional methods for the delivery of oxygenated blood or oxygen-enriched fluids to at-risk tissues involve the use of blood oxygenators. Such procedures generally involve withdrawing blood from a patient, circulating it through an oxygenator to increase blood oxygen concentration, and then delivering the blood back to the patient. One example of a commercially available blood oxygenator is the Maxima blood oxygenator manufactured by Medtronic, Inc., Minneapolis, Minn.
There are drawbacks, however, to the use of a conventional oxygenator in an extracorporeal circuit for oxygenating blood. Such systems typically are costly, complex and difficult to operate. Often a qualified perfusionist is required to prepare and monitor the system.
Conventional oxygenator systems also typically have a large priming volume, i.e., the total volume of blood contained within the oxygenator, tubing and other system components, and associated devices. It is not uncommon in a typical adult patient case for the oxygenation system to hold more than one to two liters of blood. Such large priming volumes are undesirable for many reasons. For example, in some cases a blood transfusion may be necessary to compensate for the blood temporarily lost to the oxygenation system because of its large priming volume. Heaters often must be used to maintain the temperature of the blood at an acceptable level as it travels through the extracorporeal circuit. Further, conventional oxygenator systems are relatively difficult to turn on and off. For instance, if the oxygenator is turned off, large stagnant pools of blood in the oxygenator might coagulate.
In addition, with extracorporeal circuits including conventional blood oxygenators there is a relatively high risk of inflammatory cell reaction and blood coagulation due to the relatively slow blood flow rates and the large blood contact surface area. A blood contact surface area of about 1-2 m2 and velocity flows of about 3 cm/s are not uncommon with conventional oxygenator systems. Thus, relatively aggressive anti-coagulation therapy, such as heparinization, is usually required as an adjunct to using the oxygenator.
Perhaps one of the greatest disadvantages to using conventional blood oxygenation systems is that the maximum partial pressure of oxygen (pO2) that can be imparted to blood with commercially available oxygenators is about 500 mm Hg. Thus, blood pO2 levels near or above 760 mm Hg cannot be achieved with conventional oxygenators.
Some experimental studies to treat myocardial infarction have involved the use of hyperbaric oxygen therapy. See, e.g., Shandling et al. (1997), Hyperbaric Oxygen and Thrombolysis in Myocardial Infarction: The xe2x80x9cHOT MIxe2x80x9d Pilot Study, American Heart Journal, Vol. 134, No. 3, pp. 544-550. These studies generally have involved placing patients in chambers of pure oxygen pressurized at up to 2 atmospheres, resulting in systemic oxygenation of patient blood up to a pO2 level of about 1200 mm Hg. However, use of hyperbaric oxygen therapy following restoration of coronary artery patency in the setting of an acute myocardial infarction is not practical. Monitoring critically ill patients in a hyperbaric oxygen chamber is difficult. Many patients become claustrophobic. Ear damage may occur. Further, treatment times longer than 90 minutes cannot be provided without concern for pulmonary oxygen toxicity.
For these reasons, the treatment of regional organ ischemia generally has not been developed clinically. Thus, there remains a need for a simple and convenient system for delivering oxygen-enriched blood and other fluids to patients for the localized prevention of ischemia and the treatment of post-ischemic tissue and organs.
The present invention may address one or more of the problems set forth above. Certain possible aspects of the present invention are set forth below as examples. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.
In one embodiment of the present invention, a system for the preparation and delivery of a gas-enriched fluid is provided. In applications involving the prevention of ischemia or the treatment of ischemic tissues, the system may be used for the preparation and delivery of an oxygen-enriched fluid including blood to a specific location within a patient""s body. The system may include a circuit for oxygenating or enriching blood, e.g., increasing the level of dissolved oxygen in the blood. The system includes an apparatus that combines a gas-supersaturated fluid with blood to form a gas-enriched fluid, advantageously for regional or localized delivery. The gas-supersaturated fluid may include an oxygen-supersaturated physiologic liquid, and the blood to be enriched is blood withdrawn from the patient.
The system provided further includes assemblies for supplying controlled flows or supplies of the gas-supersaturated fluid and the blood. The system includes an elongated, generally tubular assembly including a central lumen and at least one end placeable within a patient body proximate a tissue site to be treated, the end including an outlet port for the gas-enriched fluid. The system may include a catheter defining a fluid pathway, including a proximal portion adapted for coupling to supplies of gas-supersaturated fluid and blood, and a distal portion defining a fluid pathway removably insertable within a patient""s body, for infusing the gas-enriched fluid to predetermined sites.
In an alternate embodiment of the present invention, the proximal portion of the catheter is adapted for coupling to a supply of gas-supersaturated fluid, and includes a pump loop through which blood drawn from a blood inlet flows. The blood inlet comprises a porous side segment or axial sleeve defining the entry into an annular conduit that transitions into a lumen in fluid communication with the pump loop. The inlet is disposed along the portion of the catheter removably insertable within the patient""s body. Upon insertion of the catheter through an access or opening, e.g., an introducer sheath, and upon its placement within the patient body, e.g., tip placement in or proximate the coronary ostium, the blood inlet is distal to the access sheath so as to permit blood from the patient to pass through and along the fluid path defined by the blood inlet, annular conduit, lumen and pump loop before combining with the gas-supersaturated fluid to form the gas-enriched fluid delivered to the patient via the catheter central lumen and outlet port.
In another embodiment of the present invention, a method is provided for the preparation and delivery of a gas-enriched fluid. In applications involving the prevention of ischemia or the treatment of ischemic tissues, the method may include the step of combining a gas-supersaturated fluid with blood to form a gas-enriched fluid. Advantageously, the gas-supersaturated fluid comprises an oxygen-supersaturated physiologic liquid in which oxygen is dissolved at concentrations normalized to standard temperature and pressure (STP) that equal or exceed the volume of the solvent. Examples of solvents which may be used include saline, lactated Ringer""s, and other water-based physiologic solutions.
In accordance with another embodiment of the present invention, a method is provided for delivering an oxygen-enriched fluid to a specific site within a patient""s body. The method comprises raising the pO2 level of the fluid to be supplied to the patient. Where the fluid to be infused includes blood, the method may include the step of controlling or providing controlled amounts of the blood and oxygen-supersaturated fluid that are combined so as to produce an oxygen-enriched fluid for delivery to a specific predetermined site. Blood pO2 levels may be maintained, adjusted, or otherwise controlled by controlling the flow rates or by providing controlled amounts of the blood and/or oxygen-supersaturated fluid. Thus, a blood-gas control method is provided.
Furthermore, delivery of the gas-enriched fluid advantageously occurs without the formation of clinically significant bubbles. To help minimize or eliminate the formation of clinically significant bubbles, the blood contact surfaces are exposed to or coated with blood proteins for some brief time interval, usually at least several minutes, before the start of infusion of oxygen-supersaturated fluid. Also, fluid contact surfaces are exposed to or pre-wetted with liquids, e.g., saline, ethanol and benzalkonium heparin, before use. The fluid contact surfaces also do not include any substance which promotes such bubble formation, e.g., hydrophobic surfaces that are difficult to wet, teflon, teflon-composite liners, silicone oils, etc. Hydrophillic fluid contact surfaces are typically useful.
The embodiments may be used in conjunction with angiographic or guiding catheters, arterial sheaths, and/or other devices used in angioplasty and in other interventional cardiovascular procedures. The system may be used in applications involving one or more vascular openings, i.e., in either contralateral or ipsilateral procedures.
In contralateral procedures blood is withdrawn from the patient at a first location, e.g., the left femoral artery. The blood is enriched and then is returned to the patient at a second location proximate the tissue to be treated. Blood enrichment occurs as the blood pumped through the extracorporeal circuit or loop is combined with the gas-supersaturated fluid to form the gas-enriched fluid to be delivered. In applications where the system includes a catheter, the catheter may include proximal and distal ends and a central lumen. The proximal end is adapted for the catheter to receive a supply of the gas-supersaturated fluid and to receive the blood. The distal end is removably insertable within a patient""s body through a second location such as the patient""s right femoral artery. The distal end includes at least one port in fluid communication with the central lumen and through which the gas-enriched fluid may exit. Further, the distal portion of the catheter may be adapted with a tip portion shaped so as to promote insertion of the device, such as through the same sheath used for interventional procedures like angioplasty, to specific predetermined locations within a patient""s body. Examples of tip portion shapes which may be used include any of the standard clinically accepted tip configurations used with devices like guide catheters for providing access to and for holding in locations like the coronary ostium. Accordingly, the method may further include the step of positioning the portion of the distal end of the catheter including the fluid exit port at a predetermined location within a patient body proximate to the tissue to be treated.
In ipsilateral procedures, the system may be used along with one or more of any of a number of suitable, standard-size, clinically accepted guide catheters and/or introducer sheaths. The system, for example, may comprise a catheter, a catheter and guide catheter, or a catheter and sheath, for use within a guide catheter or introducer sheath used for the primary interventional procedure. In accordance with this embodiment of the present invention, blood is drawn between the catheter and guide catheter or sheath assemblies of the present invention, between the catheter assembly of the present invention and the guide catheter or introducer sheath used for the primary interventional procedure, or from the annular space between the guide catheter and the introducer sheath.
As described herein, the preferred gas-supersaturated fluid for use in accordance with the present invention is an oxygen-supersaturated fluid. However, other fluids may be used depending upon the circumstances involved in a particular desired application, such as, for example, supersaturated fluids in which one or more gases such as helium, nitrous oxide, carbon dioxide and air are dissolved. The oxygen-supersaturated fluid may include a dissolved oxygen volume normalized to standard temperature and pressure of between about 0.5 and about 3 times the volume of the solvent. The fluid is supplied to the system at a pressure of between about 250 p.s.i. and about 5000 p.s.i. The exact pressure may vary depending upon the circumstances involved in a particular application. Further, the oxygen-supersaturated fluid supplied may be a sterile fluid which does not include gas, surface, or bubble nucleation sites at which clinically significant bubbles may form.
Exemplary apparatus and methods for preparing oxygen-supersaturated fluids are disclosed in U.S. Pat. No. 5,407,426 to Spears entitled xe2x80x9cMethod and Apparatus for Delivering Oxygen into Bloodxe2x80x9d; U.S. Pat. No. 5,569,180 to Spears entitled xe2x80x9cMethod for Delivering a Gas-Supersaturated Fluid to a Gas-Depleted Site and Use Thereofxe2x80x9d; and U.S. Pat. No. 5,599,296 to Spears entitled xe2x80x9cApparatus and Method of Delivery of Gas-Supersaturated Liquidsxe2x80x9d; each of which is incorporated herein by reference. Furthermore, disclosure relating to exemplary apparatus and methods for the preparation and/or use of gas-supersaturated fluids, including, e.g., oxygen-supersaturated fluids, in various applications, may be found in the following patents and patent applications, each of which is incorporated herein by reference:
copending U.S. patent application Ser. No. 08/465,425, filed Jun. 5, 1995, which is a division of U.S. patent application Ser. No. 353,137, filed Dec. 9, 1994, now U.S. Pat. No. 5,599,296, which is a continuation in part of U.S. patent application Ser. No. 273,652, filed Jul. 12, 1994, now U.S. Pat. No. 5,569,180, which is a continuation in part of U.S. patent application Ser. No. 152,589, filed Nov. 15, 1993, now U.S. Pat. No. 5,407,426, which is a continuation in part of U.S. patent application Ser. No. 818,045, filed Jan. 8, 1992, now U.S. Pat. No. 5,261,875, which is a continuation of U.S. patent application Ser. No. 655,078, filed Feb. 14, 1991, now U.S. Pat. No. 5,086,620;
copending U.S. patent application Ser. No. 08/581,019, filed Jan. 3, 1996, which is a continuation in part of U.S. patent application Ser. No. 273,652, filed Jul. 12, 1994, now U.S. Pat. No. 5,569,180, which is a continuation in part of U.S. Patent application Ser. No. 152,589, filed Nov. 15, 1993, now U.S. Pat. No. 5,407,426, which is a continuation in part of U.S. patent application Ser. No. 818,045, filed Jan. 8, 1992, now U.S. Pat. No. 5,261,875, which is a continuation of U.S. patent application Ser. No. 655,078, filed Feb. 14, 1991, now U.S. Pat. No. 5,086,620; and
copending U.S. patent application Ser. No. 08/840,908, filed Apr. 16, 1997, which is a continuation in part of U.S. patent Ser. No. application 453,660, filed May 30, 1995, now U.S. Pat. No. 5,735,934, which is a division of U.S. patent application Ser. No. 273,652, filed Jul. 12, 1994, now U.S. Patent No. 5,569,180, which is a continuation in part of U.S. Patent application Ser. No. 152,589, filed Nov. 15, 1993, now U.S. Pat. No. 5,407,426, which is a continuation in part of U.S. patent application Ser. No. 818,045, filed Jan. 8, 1992, now U.S. Pat. No. 5,261,875, which is a continuation of U.S. patent application Ser. No. 655,078, filed Feb. 14, 1991, now U.S. Pat. No. 5,086,620.
The catheter system of the present invention is typically sized in accordance with the circumstances involved in a particular application. In general, the sizes of the various system components will be on the order of the sizes of clinically accepted interventional cardiovascular devices. Usually, the extracorporeal loop of the present invention is less than four meters in total length. Thus, for example, where the system supports blood flow rates between 100 ml/min and 175 m/min, the priming volume would be approximately 35 ml.